Most electrical appliances break down because of overheating. Overheating of an appliance or a circuit frequently causes fire or electrical shock. In order to provide a kind of protection, most houseware appliances install a fuse or a thermo cut off to prevent the overheating of the electrical wires. However, both the fuse and the thermo cut off are one time use only and can not be reset to use again. In other words, once the fuse or the thermo cut off is functioned to cut off the electric circuit, it must be replaced by a new one before the electrical appliances can function again. For the building circuitry, the bi-metal type breaker is the most common device installed in the control panel to prevent the overheating of the electrical wiring.
In other words, those conventional thermal protectors are substantially the electrical current protection to prevent overheating of the electrical wiring. However, the surrounding around the electrical appliance has nothing to protect against overheated or over-cold. For example, a pot of a coffer maker may also be overheated if there is no more coffee therein. It will also create danger of fire or breaking down situation. A halogen floor lamp would generate a great amount of heat therearound that has a high risk of burning stuff like the curtain around.
The surge protector is the most common MOV (metal oxide varistors) utilized in various electrical appliances. However, due to the fluctuation of the voltage, it may easily generate great amount of heat and may also result in explosion.
Moreover, it is well known that the CPU of a computer generates heat during operation. If the heat around the CPU accumulates to a certain extent, the CPU will be malfunctioned. Also, a heater is an appliance for generating heat. However, the user can only control the heat by setting the power output or the timer control. It is relatively expensive and difficult to control the heater according to the actual temperature around the heater.
In fact, every electrical appliance that generates heat needs a thermal guard to prevent the surrounding being overheated or over-cold. It would be a remarkable matter if there is an inexpensive device that can cut the circuit or switch off the appliance if the surrounding thereof is too hot. It not only can prolong the service life of the appliance, but also can help the user to avoid unreasonable hazard or damages.
Moreover, it would be a more advance concept to have a thermal actuator, which can easily connect with the electrical circuit of an electrical appliance without affecting the original circuit or sharing its voltage power. Besides, how to connect more than one set of thermal actuators or more than one thermal detectors thereof becomes another important and practical problem pending to be solved.